


Hamartia

by purplekitte



Series: Daemon Prince Guilliman AU [1]
Category: Horus Heresy - Various Authors, Warhammer 40.000
Genre: Alternate Universe - Canon Divergence, Community: warhammer40kink, Daemon Prince!Guilliman, Incest, Know No Fear, M/M, Warhammer Kink Meme
Language: English
Status: Completed
Published: 2013-06-12
Updated: 2013-06-12
Packaged: 2017-12-21 22:06:22
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,506
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/905487
Author URL: https://archiveofourown.org/users/purplekitte/pseuds/purplekitte
Summary: <blockquote class="userstuff">
              <p>Guilliman may have lost his soul, but he'll protect Ultramar no matter who wins the war. That means playing nice with your new allies.</p>
            </blockquote>





	Hamartia

**Author's Note:**

> Prompt: Guilliman/Kor Phaeron - his supervillain scheme actually succeeded, but perhaps he had not thought this through enough  
> daemon!Guilliman/Horus would also be good (cross-posted from the kinkmeme)
> 
> Spoilers for _Know No Fear_. If you would like my side rant about why I think this AU is dumb, it can be found [here](http://adepta-astarte.tumblr.com/post/52825301108/i-just-finished-writing-some-horus-guilliman-ill).

This had most certainly not been in Lorgar’s plan, and his shock and rage had been amusing. Horus had been surprised too, but pleasantly. He’d have to deal with the situation, of course, but one step at a time. Guilliman was much more valuable to him than Lorgar, but the latter was more erratic and inclined to make himself a nuisance.

‘Stay out of the Realm of Ultramar, all of you, and I will stay out of your affairs,’ he demanded.

‘Done.’ He chuckled. ‘You didn’t come all this way to say that, brother. What makes you think you can trust me? You know I set you up for the ambush at Calth because I considered you inconvenient. How can I trust you to not grow expansionist?’

‘You’ve changed your mind about targeting my Legion for elimination?’

‘I have no intention of casting aside an ally I could have. You’re more the changed man.’

Guilliman snorted, actual sparks lighting the shadows that surrounded him like a second cloak. Not merely black but shades and swirls of black and darker than black. His weakness had always been being too plain. He lacked charisma, and methodical competence was not nearly so inspiring. Horus had always found him boring, but he was more striking now, crowned with daemonhood.

‘What do you want of an ally then?’

‘We can coexist, you and I. I have no interest in the tedium of ruling cringing flocks you so delight in. If I have you, I have Ultramar and no need to send further armies to bring it under my banner.’

Guilliman thought--always thinking, a thousand scenarios a minute that one--and asked, ‘You’re not worried about expansionism then?’

‘Take all you want. Make of them what you will once they submit.’ _I won’t allow you the support to turn against me. Oh, you’ll always have the potential to be inconvenient, but bogged down in minutia you can only hold so much power at once. No worse than the offer you’ll get anywhere else, brother, unless you really thinking you can make it on your own. You won’t risk your kingdom making everyone your enemy._

‘Very tempting, Warmaster. I make no secret of what I want so that’s hardly a surprise. I am a straight-forward man. As long as you give me what I want, I will pledge my loyalty to you. Do not take me lightly, for I have already given up everything for what is mine once.’

What had been the truths Guilliman had seen? he wondered. Horus knew the important ones, of course, the falseness of the Emperor, the opportunities of Chaos, the path to realising one’s desires through power. Guilliman was too selfless to use it correctly. Anyone willing to martyr themselves would die because there were so many opportunities for it. It was those left behind that made the future. He had used his own soul as a bargaining chip and gotten much for it, but he squandered it away on the weak and the useless. Only by having more power than everyone else could you keep anyone from taking it away.

‘Dedication will be rewarded as surely as threats crushed.’

‘What sort of rewards?’

Horus smiled that he would ask. This Guilliman knew his own worth and had every intention of ringing every resource out of it. No more service for its own sake or blind obedience. He had had that choice: to continue to fight thanklessly on the behalf of an Imperium that would reward him and his followers with revulsion and death for what he had become or to find other protectors. The gifts of Chaos were terrible to look upon, but what corrupted the purity of Guilliman’s being was that he had chosen for his works to live when he really and truly believed he _should have_ chosen inglorious, servile death to be the man he had wanted to be. He couldn’t have arranged it better if he had purposefully orchestrated it like Prospero.

‘I can think of some, but there’s little you can be given that you couldn’t take for yourself.’

‘True.’

‘I don’t even know what you enjoy.’ Though he did know Guilliman hadn’t meant personal reward for himself. The sooner he learned the better. ‘What with you being a stoic.’

‘That’s the most diplomatic way I--’ Guilliman’s breath caught except for a sharp gasp as Horus cupped his head and brushed over the horns growing from his temples. The broken skin at their edges was still red and inflamed, hot and oozing beads of blood as Horus stroked there, and so very sensitive.

‘You enjoy that, don’t you?’

Guilliman couldn’t answer beyond a shudder, too caught between sensation and revulsion at what he had become. His eyes were still blue, almost luminous in their dark pits. Horus kissed him hard, before forcing his mouth open and exploring it with his tongue. He was reminded of Sanguinius for a moment as he found sharp fangs hidden there.

Guilliman’s hands had found their way to his shoulders by the time he pulled back. ‘Strip for me, Roboute.’

Master-crafted artificer armour was discarded piece by piece, Guilliman breathing fast but seemingly engrossed in the task. His skin was marred by patches of scale or spurs of bone, his fingers tipped in claws, festering scars wreathing his throat, but he looked good that way, spoiled but still strong.

He didn’t look away as Horus traced up and down his body with his eyes, removing his own armour, or when he touched him again. His arms went around Horus’s waist to press them together as Horus lowered him down. He had always known Guilliman would obey a direct order if it was given, but he’d never expected to have him so willing and pliant beneath him.

‘Here I thought you were a virgin.’ He wasn’t very experienced though. If Horus had to guess, he would say he had only been exposed to the pleasures of the flesh since turning. Kor Phaeron? No, it seemed unlikely, but he did have influence over Guilliman and was undoubtedly a creeper. ‘Your own sons, Roboute?’ At his blush, he knew he had been right. ‘I can see the appeal, mind you. You can show them exactly what to do, and yours are so very obedient, aren’t they? But it’s more than duty to them no matter how cold and logical they pretend to be; they’re so bright-eyed and eager to be on their knees for you, to offer themselves up for your pleasure.’

Guilliman kissed him to shut him up, biting hard enough to draw blood, then gasping and bucking into his hand as Horus wrapped it around his cock. Horus touched him firmly and expertly until he was painfully hard, not like the clumsy virgins he had had or his own hand. Meanwhile, he bent lower back to lick and suck at his other daemonic gifts, making him shudder and cry out.

Horus guided him onto his hands and knees, caressing the ridge of spikes erupting down his spine and the firm muscle of his ass.

‘Do you do this with all our brothers sworn to you?’

‘We are still brothers after all. And it’s called sealing the deal for a reason.’ Guilliman had seen the shape of ritual magic on Calth, and its consequences.

‘Then we have a deal, Warmaster,’ Guilliman agreed, as though he wasn’t already been pushing back against Horus’s fingers.

‘Good.’ Horus leaned over him and kissed the back of his neck, then bit down gently on his nape. Guilliman was strong and steady even with his weight draped across his back, but he shuddered for a moment as Horus guided himself inside.

Guilliman felt wonderful around him, tight and hot and groaning quietly. Horus reached around to jerk him as he fucked him, and Guilliman came embarrassingly quickly in his hand. Horus groaned at the sight of his uptight brother coming undone and the little broken noises he made and how he clenched around him.

Guilliman whimpered and shook but stayed still as Horus continued to take his pleasure from his body, thrusting hard and deep and finishing in his tight embrace. If only he hadn’t needed his brilliant mind for so many other things, he would have been tempted to offer him a promise of Ultramar’s safety in exchange for his body for Horus to use and abused however and whenever he wanted him. There would be time later to introduce him to debauchery and the full range of experiences and emotions a human could feel. Fulgrim could help. Or Lorgar could have a turn with him, though with the complicated mess between Horus wasn’t sure if he wanted to fuck him or be fucked by him more.

Horus kissed him possessively and stroked his hair, his horns. The shadows danced, more iridescent and excited than ever. He wanted him, but he wanted him bathed in the blood of worlds more. ‘We’re agreed then?’

‘Yes,’ he said, breathless, broken, dark and dangerous.


End file.
